This invention relates to a blast pipe for a refining nozzle. More particularly, this invention relates to a blast pipe for supplying after combustion oxygen to the space above a metal bath in a refining operation.
Refining nozzles are known which, not only include the blast pipes for delivering the supersonic primary oxygen for refining, but also possess numerous auxiliary pipes. Such auxiliary pipes are inclined between 25.degree. and 60.degree. with respect to the vertical axis (see for example Luxembourg Patent LU Nos. 78 906 and 83 814 corresponding to U.S. Pat. No. 4,434,005 which is assigned to the assignee hereof and incorporated herein by reference) and emit jets of oxygen for providing after combustion. Because these oxygen jets are subsonic, the auxiliary blast pipes are supplied by an independent oxygen circuit which permits regulation of the flow. It is also well known (see LU No. 82 846 corresponding to U.S. Pat. No. 4,366,953, assigned to the assignee hereof, all of the contents of which are incorporated herein by reference) to equip the ducts of the auxiliary pipes carrying after combustion oxygen with means to increase the degree of turbulence of the primary jet. This turbulence increasing means may consist of plates arranged within the ducts of the secondary blast pipes so as to form spirals. In other embodiments, the turbulent means comprise the walls of the ducts being provided with grooves which can be (1) circular, (2) arranged in a plane perpendicular to the axis of the duct or (3) spiralled.
In the prior art, the angles of inclination of the auxilliary blast pipes directing after combustion oxygen jets, after being determined by tests or empirical methods (taking into account the inclinations of primary oxygen jets, their arrangement, the dimensions of the converter, the height of the nozzle head above the bath, etc.), will remain constant. Thus, it is not possible to sweep the space above the bath with oxygen jets; nor it is possible to deliver after combustion oxygen into the converter at an angle dependent upon the refining phase in progress. Of course, this problem could be solved by equipping blast pipes with some sort of mechanical system enabling their angle of inclination to be modified. Unfortunately, such a system would be directly exposed to the difficult conditions existing within a converter (temperatures varying between 800.degree. and 1800.degree. C., projections of slag, of liquid metal, etc.), so as to have only a very short life. Moreover, variations of inclination obtained by mechanical means would be too slow to create an extended zone which would be virtually always supplied with oxygen.
Another disadvantage of known blast pipes is that the oxygen is delivered into the space above the bath in discrete jets. As a result, the concentration of oxygen, with respect to that of carbon monoxide, is on the one hand excessively high within the jet, and on the other hand, too low in the space between two jets. The volume above the bath in which the presence of oxygen and carbon monoxide can be ensured in essentially stoichiometric quantities to initiate and sustain combustion is thus limited.